448 
Journal of Agricultural Research 
Vol. XXV, No. IX 
SUMMARY 
(1) Studies on the pathogenicity of Corticium vagum show that the 
fungus may become a vigorous parasite on the underground parts of 
both the pea and bean. The severity of damage resulting from the 
attack of this fungus on the two plants is shown definitely to be con¬ 
ditioned by the temperature of the soil. 
(2) Corticium vagum may produce lesions on the pea through a soil 
temperature range of from 9 0 to 29 0 C. The greatest damage is found 
to result between 12 0 and 26°, with a definite optimum for tissue destruc¬ 
tion at 18°. Essentially these same temperature relations are found for 
the pathogenic action of the fungus on the bean. Within the limits 
tried (9 0 to 29.5°) neither the high nor the low temperatures entirely 
inhibited injury from the fungus on bean stems, although, in unsterilized 
soil, damage to the bean was found to be limited to temperatures of 
12.5 0 , I 5°» 18°, and 21 0 , with a maximum amount of injury at 15 0 and 18 0 . 
Plumule destruction on the two plants, except under exaggerated con¬ 
ditions, occurred only at temperatures below 21 0 . These temperature 
values are practically the same as those found for the pathogenic action 
of Corticium vagum on the potato. 
(3) Sterilized soil inoculated with a pure culture of Corticium vagum 
increased greatly the amount of injury caused by the fungus on both the 
pea and the bean. This is at variance with the results obtained in the 
studies of the potato. 
(4) The cardinal temperature for the pathogenicity of Corticium vagum 
remained the same for the various hosts—potato, pea, bean, and cotton. 
Lesions occurred on all these plants from 9 0 to 29 0 C., with a general 
optimum for tissue destruction near 18 0 . The growing-point and 
plumule destruction on the various plants was exhibited at practically 
the same range of soil temperatures for all hosts studied. These various 
temperature relations held true for all the different strains of the fungus 
used in the experiment. 
(5) The temperature requirements for the pathogenic action of Cor¬ 
ticium vagum on its various hosts appear definitely as a fixed inheritable 
characteristic of the fungus, more or less independent of the temperature 
relations of the host on which it becomes parasitic. 
(6) Corticium vagum grows in pure culture from 4.6° to 32.6° C. 
with an optimum for a period of 96 hours between 25 0 and 27 0 . The 
growth rate of the mycelium on hard agar between 23.6° and 32.6° 
decreases with the time of exposure. This fact suggests a much lower 
optimum for the continued growth of the fungus. At the lower temper¬ 
atures hyphae embed themselves in the artificial substratum and retain 
their hyalin color and active state much longer than at higher tem¬ 
peratures. At 20 0 to 30° the mycelial growth is much more superficial, 
producing aerial hyphae which grow frequently at right angles to the 
surface of the medium. This closeness of growth in contact with the 
substratum at the lower temperatures probably plays an important part 
in the ability of the fungus to attack living tissues at temperatures 
below 21 0 . 
(7) The temperature range indicated by the minimum and maximum 
temperatures for the pathogenicity of Corticium vagum approximates 
closely the temperature range found for its saprophytic activities. 
The optima for these physiological processes, however, vary widely. The 
temperature optimum for mycelial growth of the fungus, in fact, appears 
